Table 3

Possible reasons for the rise in duodenal ulceration in the nineteenth and twentieth centuries

Surveillance artefact
Environmental cofactors affecting acid secretion and tissue healing (e.g. nutritional changes, smoking, NSAID and aspirin use)
Introduction of new Helicobacterstrains
Increased acquisition of H pylorifrom non-relatives
Change in multiplicity ofHelicobacter colonisation
Improved sanitation (impediment to transmission) selected for more virulent strains
Diminished H heilmanni cocolonisation
Increase in H pylori acquisition age